A shape memory alloy (SMA) is generally a metallic material that demonstrates shape memory effects, such as the ability to return to a previous shape or size when heated and/or cooled. For example, SMAs are typically deformed at a relatively low temperature and return to a previous shape upon heating. In addition, subsequent cooling can cause the SMAs to return to the deformed shape.
Some SMAs, such as those including nickel titanium alloys (e.g., Nitinol), have different microstructures at different temperatures. The type, size and shape of the microstructure can be changed by heating, cooling and/or the application of external forces. The changes in the type, size and shape of the SMA microstructure are in part responsible for causing the shape memory effects. In addition, alloy content can influence the response of SMAs to heating, cooling and/or application of external forces.
SMAs can be employed in many applications including aircraft, piping, robotics, medical devices, optometry and dentistry.